Combined MODIS Optical Depth 047 data from the MCD19A2 product over part of west Africa, January 9, 2001.View full-size image
The MCD19A2 Version 6.1 data product is a Moderate Resolution Imaging Spectroradiometer (MODIS) Terra and Aqua combined Land Aerosol Optical Depth (AOD) gridded Level 2 product produced daily at 1 kilometer (km) pixel resolution. The MCD19A2 product provides the atmospheric properties and view geometry used to calculate the Multi-angle Implementation of Atmospheric Correction (MAIAC) Land Surface Bidirectional Reflectance Factor (BRF) or surface reflectance, MCD19A1 product.
The MCD19A2 AOD data product contains the following Science Dataset (SDS) layers: blue band AOD at 0.47 µm, green band AOD at 0.55 µm, AOD uncertainty, fine mode fraction over water, column water vapor over land and clouds, smoke injection height, AOD QA, Angstrom Exponent over the ocean, cosine of solar zenith angle, cosine of view zenith angle, relative azimuth angle, scattering angle, and glint angle. A low-resolution browse image is also included showing AOD of the blue band at 0.47 µm, created using a composite of all available orbits.
Each SDS layer within each MCD19A2 Hierarchical Data Format 4 (HDF4) file contains a third dimension that represents the number of orbit overpasses. This factor could affect the total number of bands for each SDS layer.
|File Size||~4 MB|
|Temporal Extent||2000-02-24 to Present|
|Geographic Dimensions||1200 km x 1200 km|
|Number of Science Dataset (SDS) Layers||13|
|Columns/Rows||1200 x 1200|
|Pixel Size||1000 m|
|SDS Name||Description||Units||Data Type||Fill Value||No Data Value||Valid Range||Scale Factor|
|Optical_Depth_047||Blue band (0.47 μm) aerosol optical depth over land||N/A||16-bit signed integer||-28672||N/A||-100 to 6000||0.001|
|Optical_Depth_055||Green band (0.55 μm) aerosol optical depth over land||N/A||16-bit signed integer||-28672||N/A||-100 to 6000||0.001|
|AOD_Uncertainty||AOD uncertainty based on blue-band surface brightness (reflectance)||N/A||16-bit signed integer||-28672||N/A||-100 to 30000||0.0001|
|FineModeFraction||Fine mode fraction for ocean||N/A||32-bit floating point||-99999||N/A||0 to 1000||N/A|
|Column_WV||Column Water Vapor (cm) over land||cm||16-bit signed integer||-28672||N/A||0 to 8000||0.001|
|Injection_Height||Smoke injection height (m above ground)||Meters||32-bit floating point||-99999||N/A||0 to 10000||N/A|
|AOD_QA||AOD QA||N/A||16-bit unsigned integer||0||N/A||1 to 65535||N/A|
|AngstromExp_470- 780||Angstrom Exponent 470-780nm over the ocean||N/A||16-bit signed integer||-28672||N/A||-5000 to 30000||0.0001|
|cosSZA||Cosine of Solar zenith angle (5 km)||N/A||16-bit signed integer||-28672||N/A||0 to 10000||0.0001|
|cosVZA||Cosine View zenith angle (5 km)||N/A||16-bit signed integer||-28672||N/A||0 to 10000||0.0001|
|RelAZ||Relative azimuth angle (5 km)||N/A||16-bit signed integer||-28672||N/A||-18000 to 18000||0.01|
|Scattering_Angle||Scattering Angle (5 km)||N/A||16-bit signed integer||-28672||N/A||-18000 to 18000||0.01|
|Glint_Angle||Glint Angle (5 km)||N/A||16-bit signed integer||-28672||N/A||-18000 to 18000||0.01|
The MCD19 SDS layers are three dimensional. The total number of bands in each file is contingent upon the number of orbit overpasses (1-2 bands at the equator and up to 30 bands in polar regions). For example, a file with an orbit number of five will contain five bands for each SDS layer (e.g., FineModeFraction will be recorded in 5 separate instances). Note that at high latitudes, only the first 16 orbits with the largest coverage are selected for processing per day in order to limit the file size.
Orbit information is stored in the Orbit_amount and Orbit_time_stamp attributes in the HDF file. The global metadata attributes of MODIS data products can be viewed in software such as HDFView and Panoply.
Quality assurance information should be considered when determining the usability of data for a particular science application. The ArcGIS MODIS-VIIRS Python Toolbox contains tools capable of decoding quality data layers while producing thematic quality raster files for each quality attribute.
The QC layer is stored in an efficient bit-encoded manner. The unpack_sds_bits executable from the LDOPE Tools is available to the user community to help parse and interpret the QC layers.
Product quality information is described in Section 6 of the User Guide.